Thiols are potent flavour compounds that can have an outsized impact on the hop character of IPAs, despite the fact that their concentration in beer is measured in ng/L (parts per trillion).
The main thiols are 3MH (grapefruit), 3MHA (passionfruit) and 4MMP (blackcurrant), and they are found in both bound and free forms in hops. The "bound" versions of these thiols can be released to become flavour-active by various means: in the mash (mash hopping), or by the action of (some) yeast strains.
The main way to ensure you maximise thiol expression is to keep oxygen (or pro-oxidative elements like copper and manganese) out of the mash and boil. So we modified our mash recirculation setup to eliminate splashing, treated our mash water with antioxidants like ascorbic acid (vitamin C), and even reduced our addition of yeast nutrient which contains manganese (an essential element for yeast health).
We also used mash hopping - an old technique which I wrote off as a waste of hops, until I was informed that mash enzymes can also liberate bound thiols.
Lastly, we played around with dry hop timing and temperature - some hops were added early and warm to allow yeast enzymes to liberate thiols, while the majority were added post-fermentation once the temperature of the beer had been dropped (and the yeast removed).
We avoided unmalted grains and crystal malts for this recipe, and they can inhibit thiol expression. We also used chit malt, as this has high levels of LTP1 protein which both contains (bound) thiols and protects against their degradation by oxidation.
As for yeasts, we co-pitched Lallemand Verdant IPA and Lallemand BRY-97 (both dry yeasts) because they're each high in one of the enzymes important in biotransformation (ie. the creation of new flavour compounds during fermentation).
Total hopping rate was just over 21g/L, which makes it the hoppiest beer we've brewed.
We were also very careful in our selection of hop varieties.
Cascade: a classic hop high in the bound form of 3MH (grapefuit) thiol which is why we used it in the mash.
Idaho 7: very high in a hop ester called 2MiB (apricot, peach) which has a synergistic effect with some thiols. We used LupoMax™ which is a concentrated form of hop pellets.
Motueka: NZ hop known to be high in some unique thiols.
Galaxy: Aussie hop that is also quite high in the thiols that Idaho 7 is low in, covering our bases in terms of getting that saturated hop character.
Citra: also quite high in thiols, especially 4MMP (blackcurrant) which can have a synergistic effect on some other hop aromatic compounds linalool and geraniol (floral, citrussy aromas).
Did it work?
As you can see, we've brought together quite a bit of theoretical hop science in creating this beer. But did it actually work in practice..?
I'm pleased to say that (in my opinion) IPA Theory #1 is one of our best beers to date. It's impossible to say whether all of our experimental techniques had the effects that we were aiming for, but there's a depth to the hop character in this beer that I'm extremely happy with.
We'll definitely be adopting some of these methods in future brews.